High Entropy Alloy Having Composite Microstructure and Method of Manufacturing the Same

ABSTRACT

A method of making a metallic alloy, more particularly, a high-entropy alloy with a composite structure that exhibits high strength and good ductility, and is used as a component material in electromagnetic, chemical, shipbuilding, machinery, and other applications, and in extreme environments, and the like.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of application Ser. No. 15/455,649,filed Mar. 10, 2017, which claims the benefit of Korean PatentApplication No. 10-2016-0029570, filed on Mar. 11, 2016, the disclosuresof which are hereby incorporated in their entirety by reference.

BACKGROUND OF THE INVENTION Field of the Invention

The present disclosure relates to a metal alloy for a component materialused in electromagnetic, chemical, shipbuilding, machinery, and otherapplications, in addition to components, structural materials, and thelike, used in an extreme environment and, in particular, to ahigh-entropy alloy having a composite structure.

Description of Related Art

Due to technological breakthroughs in industrial technology, metals andalloys according to the related art have limitations in meetingcharacteristics required for various materials. To satisfy requirementsfor multi-functionality, as a novel alloy, a new type of materialreferred to as a high-entropy alloy has recently been proposed anddeveloped.

A high-entropy alloy refers to not a compound formed by reducing freeenergy due to the formation of an intermetallic compound, but an alloywith a ductile single phase or multi-phase structure formed by reducingtotal free energy due to a significant increase in configuration entropyby mixing several elements. In other words, a high-entropy alloy refersto not an intermetallic compound or an amorphous alloy with negligibleor limited ductility consisting of multi-component alloying elements,but an alloy with solid solution matrix formed by an atomic scalemixture of several alloying elements without any significantpreferential attraction between specific elements.

A high-entropy alloy is disclosed in Non-Patent Document 1 (MaterialsScience and Engineering A, Vol. 375-377, 2004, page 213-218). InNon-Patent Document 1, a multi-element alloy, Fe₂₀Cr₂₀Mn₂₀Ni₂₀Co₂₀, thatthe researchers expected to form an amorphous phase or complexintermetallic compound, unexpectedly form a single-phase crystallineface-centered cubic (FCC) solid solution, thereby attracting theinterest of material scientists and engineers. Most high-entropy alloysexhibit unusual characteristics such as the formation of a single phasestructure, even when alloying elements are mixed in similar amounts in aquartenary, quinary, or higher system, in contrast to the conventionalalloy systems in which minor additional alloying elements are added to amajor alloying element with the content over 60 weight % to 90 weight %in order to induce precipitates or particles. Unique characteristics arealso found in an alloy system in which configuration entropy due tomixing is high.

A high-entropy alloy contains four or more types of metallic elementshaving an atomic content between 5 at. % and 35 at. %, and is an alloysystem in which all alloying elements behave as a main element. Due to asimilar atomic fraction of elements existing in an alloy, a high degreeof mixing entropy is induced. Therefore, instead of the formation ofbrittle intermetallic compound or an intermediate compound, a solidsolution having a stable and simple structure at high temperature isformed.

As prior art related to high-entropy alloys, there are provided PatentDocument 1 (U.S. Laid-Open Patent No. US 2013/0108502 A1) and PatentDocument 2 (U.S. Laid-Open Patent No. 2009/0074604 A1). In PatentDocument 1, disclosed is a high-entropy alloy having a high degree ofhardness and high modulus, an alloy system containing five or more typesof metallic elements, in which each element such as vanadium (V),niobium (Nb), tantalum (Ta), molybdenum (Mo), titanium (Ti), or the likeis included with a deviation of ±15 atomic % or less, and in which thereis no distinction between major and minor elements because of thesimilar atomic contents in the alloy. In addition, the high-entropyalloy is formed as a single phase solid solution having a face-centeredcubic and/or body-centered cubic structure. However, in Patent Document1, different types of relatively expensive and heavy alloying elementsare added, and a difficulty in a manufacturing process is expected dueto a large difference in melting points among added alloying elements.

Meanwhile, in Patent Document 2, disclosed is a high-entropy alloyhaving a high degree of hardness, manufactured in a powder metallurgyprocess using a ceramic phase (representatively, tungsten carbide) andmulti-component high-entropy alloy powder. The high-entropy alloy withhard ceramic particles is manufactured with the single phase solidsolution matrix embedded with hard ceramic particles, having highstrength and excellent high temperature properties. However, in PatentDocument 2, since a high temperature process is required when a ceramicmaterial is used to manufacture an alloy with hard ceramic particles, aproblem associated with high temperature sintering process such as lowtoughness is expected to occur due to the presence of the interfacedefects.

SUMMARY OF THE INVENTION

An aspect of the present disclosure provides a high-entropy alloy with acomposite structure, without a relatively expensive and heavy alloyingelement or ceramic element being added thereto, having excellentstrength and ductility through microstructure modification of thehigh-entropy alloy, by inducing partial phase separation and thecomposite structure with a soft second phase and maintaining ahigh-entropy solid solution matrix by heat treatment and deformationprocessing, and a method of manufacturing the same.

According to an aspect of the present disclosure, a high-entropy alloyhaving a composite structure, includes: by weight %, iron (Fe) greaterthan 5% to 35% or less, manganese (Mn) greater than 5% to 35% or less,nickel (Ni) greater than 5% to 35% or less, and cobalt (Co) greater than5% to 35% or less, and includes at least one of copper (Cu) greater than3% to 40% or less and silver (Ag) greater than 3% to 40% or less,wherein a ductile second phase is distributed in a matrix of thehigh-entropy alloy.

According to another aspect of the present disclosure, a method ofmanufacturing a high-entropy alloy having a composite structure,includes: preparing a metallic material comprising, by weight %, Fegreater than 5% to 35% or less, Mn greater than 5% to 35% or less, Nigreater than 5% to 35% or less, and Co greater than 5% to 35% or less,and including at least one of Cu greater than 3% to 40% or less and Aggreater than 3% to 40% or less; manufacturing an alloy by melting themetallic elements having been prepared in one of casting, arc melting,and powder metallurgy methods; homogenization heat treatment having beenmanufactured; and cooling the alloy after the homogenization heattreating.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawings will be provided by the Office upon request and paymentof the necessary fee. The above and other aspects, features, andadvantages of the present disclosure will be more clearly understoodfrom the following detailed description taken in conjunction with theaccompanying drawings, in which:

FIGS. 1A and 1B are diagrams illustrating a microstructure of ahigh-entropy alloy with a composite structure according to the presentdisclosure. FIG. 1A illustrates a microstructure before deformationprocessing including rolling, drawing and extrusion, and

FIG. 1B illustrates a microstructure after deformation processing;

FIGS. 2A and 2B are images of microstructures of inventive examples 3and 4, respectively;

FIGS. 3A and 3B are images of microstructures of inventive examples 1and 2, respectively;

FIG. 4 is a flowchart illustrating an example of a manufacturing methodaccording to the present disclosure;

FIGS. 5A and 5B are images of microstructures of inventive example 5,respectively;

FIG. 6A is a scanning electron microscope image of a microstructureafter casting of inventive example 1, and FIGS. 6B through 6F areelemental mapping images of Mn, Fe, Co, Cu, and Ni alloying elements,respectively for FIG. 6A;

FIG. 7A is an electron microscope image of a microstructure afterprocessing of inventive example 1, and FIGS. 7B through 7F are elementalmapping images of Mn, Fe, Co, Cu, and Ni alloying elements,respectively, for FIG. 7A; and

FIG. 8 is an XRD analysis graph of inventive example 1.

DETAILED DESCRIPTION OF THE INVENTION

The inventors of the present disclosure conducted research into a methodof improving mechanical/physical characteristics such as strength,ductility, and the like of a high-entropy alloy. As a result, comparedto an alloy in which various alloy elements form a single-phaseface-centered cubic or body-centered cubic solid solution, when somecompositions of various alloy elements were partially separatedtherefrom or a different ductile metallic phase was formed instead ofhard brittle intermetallic compounds, or when segregation or partialphase separation into ductile phase occurred, it was recognized thatductility and strength were further increased after deformationprocessing. In addition, when a fine filament structure was distributedthrough deformation processing, it could be confirmed that ahigh-entropy alloy with excellent strength and ductility was formed,leading to the present disclosure.

Hereinafter, a high-entropy alloy with a composite structure accordingto the present disclosure will be described in detail. First, acomposition of a high-entropy alloy according to the present disclosurewill be described in detail.

A high-entropy alloy according to the present disclosure includes, byweight %, iron (Fe) greater than 5% to 35% or less, manganese (Mn)greater than 5% to 35% or less, nickel (Ni) greater than 5% to 35% orless, and cobalt (Co) greater than 5% to 35% or less, and it ispreferable to include at least one of copper (Cu) greater than 3% to 40%or less and silver (Ag) greater than 3% to 40% or less.

Fe, Mn, Ni, and Co are elements forming a high-entropy alloy, are period4 transition elements, and are elements suitable for formation of asolid solution, or the like, since a difference in atomic radii, and thelike, is small. Mn and Ni are elements promoting formation of aface-centered cubic (FCC) solid solution, and Co promotes refinement ofa structure. Here, the content of the elements being greater than 5% to35% or less is to induce a change in a portion of entropy in a uniformand homogeneous microstructure, in which a degree of entropy issignificantly increased by as much as possible, high enough forformation of a solid solution.

Meanwhile, Cu and Ag are elements not for formation of a complete solidsolution with Fe, Mn, Ni, and Co, but for partial separation and theformation of a ductile phase to be separated therefrom. Thus, theelements serve to increase ductility, and serve to enhance strength as afilament is formed by elongating the phase after deformation processing.Here, the content of Cu and Ag being greater than 3% to 40% or less isto induce an increase in ductility and strength due to partialseparation of the ductile second phase, depending on fraction of aseparated phase.

Hereinafter, a microstructure of a high-entropy alloy according to thepresent disclosure will be described in detail. FIG. 1 is a diagramschematically illustrating a microstructure of a high-entropy alloyaccording to the present disclosure, and the present disclosure will bedescribed in detail with reference to FIG. 1.

In a microstructure of a high-entropy alloy according to the presentdisclosure, it is preferable that a ductile second phase be distributedin a matrix, a single phase solid solution, as illustrated in FIG. 1A.Meanwhile, after deformation processing so as to turn the ductile secondphase into elongated filaments, as illustrated in FIG. 1B, in ahigh-entropy alloy according to the present disclosure, it is preferablethat a filament structure formed by stretching a ductile second phase bedistributed in a matrix.

The matrix refers to a solid solution formed by elements such as Fe, Mn,Ni, and Co.

The second phase refers to various forms or structures, not solidifiedin the matrix, such as a solid solution of a phase having a differentelement (a second solid solution), a single phase dendrite, segregation,a phase separation region, a particle, and the like. In other words, thesecond phase may refer to a structure different from the matrix. Thesecond phase is distributed, thereby allowing a high-entropy alloy toensure excellent ductility and strength through distribution of ductilesecond phase particles, filaments and other forms of ductile secondphase.

The second phase is a Cu-rich phase (Cu—Mn—Ni phase) or an Ag-rich phase(Ag—Mn phase), which is not fully dissolved in the matrix of ahigh-entropy alloy, a solid solution. The phase described above is aphase having ductility higher than that of a matrix after casting,thereby having an effect of increasing ductility of a high-entropyalloy. Meanwhile, after deformation processing such as rolling, drawing,extrusion or the like of a high-entropy alloy, the phase described aboveis stretched to be elongated as a filament, thereby enhancing thestrength.

The second phase exists while having a width of 5 μm to 20 μm and alength of 30 μm to 300 μm before processing, as illustrated in FIGS. 2Aand 3A. Meanwhile, as illustrated in FIGS. 2B and 3B, after processing,the second phase is stretched. Thus, the second phase exists as anelongated filament having a thickness of 0.05 μm to 2 μm and a length of10 μm to 1000 μm, and thus, a matrix may be strengthened. When thefilament exists while having a thickness of 0.05 μm to 2 μm and a lengthof 10 μm to 1000 μm, the filament is not damaged by deformation anddeformation resistance is optimized, thereby enhancing strength. Thestretched filament exists to be elongated in a high-entropy alloy, andthus, an interface existing as an obstacle to deformation is provided.Thus, the filament serves to strengthen a matrix of a high-entropyalloy.

In the case of a high-entropy alloy having a filament structure due tothe processing, a technical effect of simultaneously improving strengthand ductility may be provided.

Hereinafter, a method of manufacturing a high-entropy alloy according tothe present disclosure will be described in detail. FIG. 4 illustrates aschematic procedure of a manufacturing method according to an exemplaryembodiment. Next, a manufacturing method according to the presentdisclosure will be described in detail with reference to FIG. 4.

According to the present disclosure, preparing a metal materialincluding, by weight %, Fe greater than 5% to 35% or less, Mn greaterthan 5% to 35% or less, Ni greater than 5% to 35% or less, and Cogreater than 5% to 35% or less, and including at least one of Cu greaterthan 3% to 40% or less and Ag greater than 3% to 40% or less, isincluded therein; and melting, homogenization heat treating, and coolingare also included. Processing a high-entropy alloy manufactured therebymay be added thereto.

The melting process is provided to alloy a manufactured metallicmaterial, a method therefor is not particularly limited in the presentdisclosure, and a method commonly used in a technical field of thepresent disclosure may be used. For example, the alloy may bemanufactured in casting, arc melting, powder metallurgy, and othermethods.

Next, the manufactured alloy is homogenization heat treated.Homogenization is a process for inducing diffusion, and it is preferableto maintain an alloy in a temperature range of 900° C. to 1200° C. for 1hour to 48 hours.

Cooling is performed after the homogenization heat treating. A coolingmethod is not particularly limited, and a method of air-cooling,water-quenching or furnace-cooling may be performed. Through the coolingprocess, a phase, in which some compositions are separated from amicrostructure or having ductility of a different composition, may beformed. Alternatively, segregation or phase separation may occur. Thus,forming a small precipitate.

With respect to a high-entropy alloy manufactured in the methoddescribed above, further processing may be performed. In the presentdisclosure, a deformation processing method is not particularly limited,and a processing method according to the related art performed in atechnical field of the present disclosure may be applied. For example,hot working, rolling, drawing, room temperature processing, and the likemay be used. By the deformation processing, as illustrated in FIG. 1B, asecond phase inside a high-entropy alloy matrix is changed into afilamentary structure. In other words, when deformation processing isperformed, a high-entropy alloy according to the present disclosure hasa technical effect of simultaneously improving strength and ductility.

Hereinafter, an exemplary embodiment of the present disclosure will bedescribed in detail. An exemplary embodiment described below is merelyto provide an understanding of the present disclosure, and the presentdisclosure is not limited thereto.

Exemplary Embodiment

First, as illustrated in Table 1, high-entropy alloys with the compositestructure, according to comparative examples 1 through 3 and inventiveexamples 1 through 5, were manufactured.

A metal material having a composition (by weight %) of Table 1 wasprepared, and the metal material was arc melted in air or a vacuum orargon atmosphere to manufacture an alloy. Thereinafter, homogenizationheat treatment was performed at 1050° C. for 24 hours.

Meanwhile, with respect to the high-entropy alloys with the compositestructure manufactured as described above, according to comparativeexamples 1, 2, and 3 and inventive examples 1, 2, 3, 4, and 5,deformation processing including rolling was performed at roomtemperature to manufacture a board having a thickness of 1 mm.

With respect to the high-entropy alloys manufactured as described above,a tensile test was carried out and mechanical properties were evaluated.The mechanical properties are illustrated in Table 1.

TABLE 1 Tensile Yield strength strength Elongation Classification AlloyMicrostructure (MPa) (MPa) (%) Comparative Co₂₀Cr₂₀Fe₂₀Mn₂₂Ni₁₈ Singlephase 620 480 40 example 1 Comparative Fe₂₅Ni₂₅Co₂₅Cr₂₅ Single phase1000 870 35 example 2 Comparative Fe₂₀Mn₂₀Ni₂₀Co₂₀Cr₂₀ Single phase 760640 17 example 3 Inventive Fe₂₀Ni₂₀Co₂₀Mn₂₀Cu₂₀ Matrix + dendrite 1020730 46 example 1 Inventive Fe₂₀Ni₂₀Co₂₀Mn₂₀Cu₂₀ Matrix + filament 16331460 32 example 2 Inventive Fe₂₀Ni₂₀Co₂₀Mn₂₀Ag₂₀ Matrix + Ag-rich phase1080 923 43 example 3 Inventive Fe₂₀Ni₂₀Co₂₀Mn₂₀Ag₂₀ Matrix + filament1794 1645 29 example 4 InventiveFe_(17.5)Ni_(17.5)Co_(17.5)Mn_(17.5)Cu₃₀ Matrix + filament 1435 1225 21example 5

As illustrated in Table 1, in the case of inventive example 1 includinga second phase (a dendrite) in a matrix and inventive example 3including an Ag-rich phase in a matrix, while satisfying a compositionaccording to the present disclosure, strength was excellent, as comparedto a comparative example. In addition, elongation exceeded 40%, andthus, excellent ductility was confirmed. In the case of inventiveexamples 2, 4, and 5, having a structure of a filament formed bystretching a ductile second phase by deformation processing, highstrength and excellent elongation were ensured.

Meanwhile, FIGS. 2A and 2B are images of inventive examples 3 and 4,respectively. In FIG. 2A, a microstructure before deformation processingis confirmed that an Ag-rich phase, not fully solidified in a matrix,exists in the matrix. In FIG. 2B, a microstructure after deformationprocessing is confirmed that the Ag-rich phase has a filament structure.

FIGS. 3A and 3B are images of inventive examples 1 and 2, respectively.In FIG. 3A, a microstructure before deformation processing is confirmedto have a structure in which a dendrite phase exists in a matrix. InFIG. 3B, a microstructure after deformation processing is confirmed tohave a filament structure in which the dendrite phase is thinlyelongated.

In addition, FIGS. 5A and 5B are images of inventive example 5. In FIG.5A, a microstructure before deformation processing is confirmed to havea structure in which a dendrite phase exists in a matrix. In FIG. 5B, amicrostructure after deformation processing is confirmed to have afilament structure the Cu-rich phase (Cu—Mn—Ni phase) is thinlyelongated.

Meanwhile, FIG. 6A is an electron microscope image of a microstructureafter casting of inventive example 1. FIGS. 6B through 6F are images ofa mapping image of Mn, Fe, Co, Cu, and Ni alloying elements,respectively. In addition, in Table 2, energy dispersive spectroscopy(EDS) analysis values with respect to compositions measured in adendrite arm and a matrix of inventive example 1 are summarized.

TABLE 2 Mn Fe Co Ni Cu (at. %) (at. %) (at. %) (at. %) (at. %) Matrix19.5 21.28 22.13 19.12 18.43 Dendrite 24.97 5.01 5.71 13.14 51.18 arm

As illustrated in FIG. 6 and Table 2, Cu and Mn are significantlydistributed in a dendrite arm, and Co and Fe alloying elements aremainly distributed in a matrix between dendrite arms. In addition, a Nialloying element is confirmed in a dendrite arm, but mainly distributedin a matrix. In addition, Fe and Co are mainly distributed in a matrixbetween dendrite arms, but the high content of other alloying elements(Mn, Ni, and Cu), and the like is confirmed. A main alloying element ofa dendrite arm is Cu, and a significant amount of Mn and Ni alloyingelements is also included therein. Since melting temperatures of Cu andMn are lower than melting temperatures of Fe and Co, Cu and Mn have atendency to be separated while being solidified at the beginning. Thus,Cu and Mn may grow as a Cu—Mn dendrite. A melting temperature of an Nialloying element is higher than melting temperatures of Cu and Mnalloying elements. However, since solid solubility of the Ni alloyingelement with respect to Cu is significant, a solid solution phase of Niand Cu is distributed in a matrix in a manner similar to a Cu phase. Cuand Mn form a solid solution at a high temperature (>900° C.). When thecontent of Mn exceeds 20%, the solid solution is separated into twophases below 700° C.

FIG. 7A is an electron microscope image of a microstructure afterprocessing of inventive example 1, and FIGS. 7B through 7F are imagesillustrating a mapping image of Mn, Fe, Co, Cu, and Ni alloyingelements, respectively.

As illustrated in FIG. 7, a filament structure formed by stretching aCu-rich phase (Cu—Mn—Ni phase), a ductile second phase after deformationprocessing, is confirmed. A matrix phase and the Cu-rich phase (Cu—Mn—Niphase) have an FCC structure. When lattice constants of two phases arecalculated using Vegard's rule, using elements of Table 1, a differencein a size of lattice constants of two phases is not significant. In XRDspectra, it is difficult to observe phase separation.

FIG. 8 is a graph illustrating an XRD analysis result of inventiveexample 1. In FIG. 8, diffraction peaks are illustrated as (111), (200),(220), and (311), respectively, and refers to a FCC crystal structurehaving a lattice constant, a=0.348 nm. In other words, as other peaksare not observed, a FCC crystal structure is confirmed after as-cast andhomogenization treatment. In addition, as a portion of a peak (220) isseparated on XRD data, it is confirmed that a second phase exists.

As set forth above, according to an exemplary embodiment, through acombination of a matrix and a ductile second phase of a high-entropyalloy, in addition to a shape, a size, and distribution by deformationprocessing of a ductile phase, excellent strength and ductility may beimplemented. Thus, it is advantageous to variously use a high-entropyalloy.

While exemplary embodiments have been shown and described above, it willbe apparent to those skilled in the art that modifications andvariations could be made without departing from the scope of the presentinvention as defined by the appended claims.

What is claimed is:
 1. A method of manufacturing a high-entropy alloyhaving a composite structure, comprising: preparing metallic elementscomprising, by weight %, Fe greater than 5% to 35% or less, Mn greaterthan 5% to 35% or less, Ni greater than 5% to 35% or less, and Cogreater than 5% to 35% or less, and comprising at least one of Cugreater than 3% to 40% or less and Ag greater than 3% to 40% or less;manufacturing an alloy by melting the metallic elements having beenprepared in one of casting, arc melting, and powder metallurgy methods;homogenization heat treating the alloy having been manufactured; andcooling the alloy after the homogenization heat treating.
 2. The methodof manufacturing a high-entropy alloy having a composite structure ofclaim 1, wherein the homogenization heat treating is performed while thealloy is maintained in a temperature range of 900° C. to 1200° C. for 1hour to 48 hours.
 3. The method of manufacturing a high-entropy alloyhaving a filamentary composite structure of claim 1, further comprising:performing deformation processing, wherein the deformation processingincludes hot working, rolling, drawing, at room temperature and elevatedtemperatures.